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- Thanks for the suggestion. The transistors were on-hand. Ultimately once I understand the concepts from "first principles" / discrete components, then I'd just replace the whole lot with either a motor driver circuit or a dedicated H-bridge. The table at the bottom of the circuit you suggest indicates I need to switch pins between VCC/GND/Disconnected. How can linking 1-2 attached to a pin and 3-4 attached to another pin give me full control? (Code isn't setting both high, but I'll attach it anyway)RickMeasham– RickMeasham2014-12-28 22:43:36 +00:00Commented Dec 28, 2014 at 22:43
- 1The point of the H-Bridge is that the transistors work in pairs - so you would have 1&2 or 3&4 on together, but never 1&3 or 2&4 - if you go back to 'Design 1' you will observe that a single input has been put through an inverter stage to ensure this doesn't happen - your re-design replaces that with software - OK 'til a bug sets up a short.. So with the standard arrangement on that link, the truth table at the bottom (disregard the not-connected options) shows you the combinations. You have off/brake/forward/backward and possibly PWM as well..Mark Williams– Mark Williams2014-12-28 23:51:46 +00:00Commented Dec 28, 2014 at 23:51
- No diodes at home, so I built it on circuit.io: 123d.circuits.io/circuits/511807-h-bridge where I had the exact same problem as my original circuit. Until I realised the NPNs were in backwards. Then everything came good. Going to check my original circuit tomorrow and see if I did the same there before I rebuild.RickMeasham– RickMeasham2015-01-02 11:28:23 +00:00Commented Jan 2, 2015 at 11:28
- Turns out my actual problem was having the transistors around the wrong way. I couldn't get my circuit to work so I built yours and got exactly the same thing. The above circuits.io result gave me a clue so I played with them and got them around the right way. Turns out that the side that appears flat in Fritzing is the round side and vice-versa.RickMeasham– RickMeasham2015-01-13 11:42:57 +00:00Commented Jan 13, 2015 at 11:42
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